Films provided with several coating layers and the use thereof in automobile manufacturing

ABSTRACT

The present invention relates to films coated with two or more coats, wherein 
     A the surface of a plastic film having a thickness of from 10 to 500 μm is coated if desired with a filler composition, 
     B the surface of the plastic film, or the filler coat, is overcoated with at least one pigmented paint coat, 
     C the pigmented paint coat is coated if desired with a transparent plastic film.

The present invention relates to films coated with two or more coats, toa process for preparing these films, and to the use of the films inautomotive construction

EP-A-374 551 discloses coated substrates which are suitable forproducing add-on parts for car bodies. The coated substrates describedin EP-A-374 551 consist of metal panels which have been coated with atleast one paint coat or of composite materials whose surface layerconsists of the coated metal panels.

P4424290.9 discloses substrates coated with two or more coats. Thesesubstrates are deformed and are processed further if desired with theaid of additional materials. In this way it is possible to produceadd-on parts for vehicle bodies.

The object of the present invention was to provide films, coated withtwo or more coats, which can be applied to molding blanks, preferablymetal panels prior to their deformation, which have improved propertiesfollowing the deformation of the blanks, relative to the coatedsubstrates disclosed in EP-A-374 551, and in whose preparation onlysmall amounts of solvent are emitted and simple quality monitoring ispossible.

This object is achieved in accordance with the invention by theprovision of films coated with two or more coats, wherein

A the surface of a plastic film having a thickness of from 10 to 500 μmis coated if desired with a filler composition,

B the surface of the plastic film, or the filler coat, is coated with atleast one pigmented paint coat,

C the pigmented paint coat is coated if desired with a transparentplastic film.

A film which can be peeled off is applied if desired onto thetransparent plastic film and/or the pigmented paint coat and/or theuncoated side of the base film.

The present invention also relates to a process for preparing a filmcoated with two or more coats, which comprises

A coating the surface of a plastic film having a thickness of from 10 to500 μm, if desired, with a filler composition suitable for coating carbodies,

B coating the surface of the plastic film, or the filler coat, with atleast one pigmented paint coat,

C if desired, coating the pigmented paint coat, if appropriate, with atransparent plastic film, and

D curing the paint coat applied to the surface of the plastic film orthe filler coat applied to the surface of the plastic film.

In this process, the curing of the filler coat applied in step A can becarried out before overcoating with at least one pigmented paint coat,and the curing of the pigmented paint coat applied in step B can becarried out before applying the transparent plastic film. If desired, aprotective film which can be peeled off can be applied after step C orD.

A further subject of the present invention is the use of the novelcoated films for coating molding blanks to produce vehicle bodies,preferably car bodies, and to produce build-on parts for vehicle bodies.Consequently, it is preferred in accordance with the invention to employcoating materials and filler compositions which are suitable for carbodies, provided they have sufficient flexibility for the purposes ofthe invention, i.e. provided the cured coating systems have T-bendvalues of ≦3.0 preferably ≦2.0 and, with particular preference, ≦1.0.

The car bodies coated with the novel films are notable for very highresistance to stone chipping and corrosion. Further advantages of thenovel coated films are that they can be produced on installationsrequiring little space. Moreover, owing to the use of painted plasticfilms for the coating of bodywork, only very small amounts of organicsolvent are emitted. Advantageously, therefore, quality monitoringbegins with the painted plastic film, whereas in the case ofconventional painting of metal panels the quality of the coating cannotbe assessed until after the application of the coats of paint to thesubstrate, and in the case of quality defects the painted substrate as awhole has to be discarded.

In the preparation of the novel films it is primarily thermoplasticswhich are suitable. In step A it is possible to employ a film made froma polyolefin, a polyamide, a polyurethane, a polyester, a polyacrylate,a polycarbonate or a mixture of different polymeric substances. Theplastic film employed in step A has a thickness of 10-500, preferably20-250 μm and may comprise dyes and/or pigments.

Corresponding materials can also be employed as a film which can bepeeled off.

Insofar as the plastic film is employed for use for vehicle bodies andfor that purpose is additionally to be coated with a filler composition,it is preferred to use filler compositions which are suitable for thecoating of car bodies. Here too, there must be sufficient flexibilityfor the purposes of the invention. In accordance with the invention thisflexibility can be controlled by way of the degree of crosslinking.

In the conventional painting of car bodies, the primer applied byelectrodeposition is overcoated with a filler composition. The fillercoat obtained in this way has essentially two functions: on the onehand, it is intended to compensate for the unevennesses of theelectrodeposition primer and, on the other hand, it is intended toimprove the stone-chip resistance of the overall coating. The fillercompositions consist essentially of a binder, a crosslinking agent,pigments and fillers and, if desired, further additives, for examplecrosslinking catalysts and leveling assistants.

The filler compositions which can be employed may comprise as binder,for example, epoxy resins, polyester resins, polyurethane resins,polyacrylate resins and alkyd resins or combinations of such resins. Ascross-linking agent the filler compositions which can be employed maycomprise amino resins, for example melamine-formaldehyde resins, amines,polyisocyanates and carboxyl-containing compounds. Examples of pigmentswhich may be present in the filler compositions which can be employedare titanium dioxide, phthalocyanines, iron oxides and carbon black.Fillers which can be present in the filler compositions are, forexample, lime or barium sulfate.

The moldings coated with the novel films, for example car bodies,surprisingly have a good resistance to stone chipping even when nofiller composition is applied in step A.

In step B, at least one pigmented top coat is applied to the surface ofthe plastic film or to the filler coat which is obtained after step Ahas been carried out.

For this purpose it is possible to use any base coat or top coatsuitable for the conventional painting of car bodies. A prerequisitehere too, however, is good flexibility of the cured coating, without theloss of resistance to stone chipping and corrosion. Coating materials ofthis kind are well known to the skilled worker. They essentiallycomprise a polymeric binder, with or without a crosslinking agent, and apigment or mixture of pigments.

The top coat or base coat employed in step B can comprise as binder, forexample, a polyester resin, a polyurethane resin or a polyacrylate resinor a mixture of such binders. As crosslinking agent the top coat or basecoat can comprise an amino resin, a polyisocyanate resin, acarboxyl-containing crosslinking agent or a mixture of such crosslinkingagents. Examples of pigments which may be present in the pigmented topcoat or base coat applied in step B are titanium dioxide, phthalocyaninepigments, carbon black, iron oxide pigments, aluminum flake pigments andpearlescent pigments.

In step C, a transparent plastic film is applied to the paint coatapplied in step B. It is possible here in principle to employ thematerials which are also suitable for the base film.

In step D, the paint coat applied to the surface of the plastic film, orthe paint coats applied to the surface of the plastic film, is or arecured, in which case the curing of the filler coat applied in step A canbe carried out before overcoating with at least one pigmented paintcoat, and the curing of the pigmented base coat applied in step B can becarried out before coating with the transparent plastic film. It is alsopossible to overcoat the filler coat applied in step A, in the uncuredstate, with a base coat and then to cure filler coat and base coattogether before applying the transparent plastic film. The paint coatsare normally cured by heating at temperatures from 60 to 230° C. On suchheating there is a reaction between the binders and crossslinking agentspresent in the paints, and three-dimensional polymer networks are formedwhich give the paint surface a particularly high resistance tomechanical or chemical attack.

The paint coats can be applied, for example, by spraying, roller coatingor knife coating.

The films coated in accordance with the invention can be rolled up. As aresult, the products can be sold and supplied in the form of rolls. Forthis reason, the coating materials employed in accordance with theinvention must have a flexibility sufficient for rolling up.

The films can be applied in principle to all molding blanks, preferablymetal panels suitable for producing vehicle bodies, build-on parts forvehicle bodies, domestic appliances, for example refrigerators, washingmachines and dishwashers. The films are applied predominantly topretreated metal panels. These can have been pretreated, for example, byphosphating and/or chromating.

The coated plastic films prepared as described above can be laminatedonto the surface of a molding blank, i.e. of a substrate which has notyet been deformed, preferably metal sheet. In this case the film canfirst be laminated onto the undeformed substrate which can then bedeformed and, finally, coated.

The metal sheet can be coated in succession with a base film, a fillerif desired, a pigmented paint and, if desired, a transparent plasticfilm. From the metal sheet coated in this way, which can be stored andsupplied in roll form, automotive parts are cut out and shaped.

Alternatively, the base film is first of all coated in succession with afiller, if desired, with a pigmented paint and, if desired, with atransparent plastic film. This coat system is laminated onto a metalsheet from which automotive parts are produced by cutting out andforming. The requirements regarding the flexibility of the coatingmaterials employed must, consequently, also be oriented toward theabove-described application techniques.

Adhesion to the surface which is to be coated can be brought about invarious ways. One possibility, for example, is to employ films havingadhesion-promoting groups, for example urethane groups, acid anhydridegroups or carboxyl groups, or films which have beer provided withadhesion-promoting groups by coextrusion with a polymer which containsadhesion-promoting groups. Adhesion between the film and the surface tobe coated can also be achieved by using an adhesive. In this case it ispossible to employ both adhesives which are solid at room temperatureand adhesives which are liquid at room temperature.

When applying films having adhesion-promoting groups by lamination, thesubstrate is generally covered with the film such that the adhesionpromoter layer contacts the surface which is to be coated. By applyingpressure and heat the film is then laminated onto the surface which isto be coated. The pressure and temperature here should be chosen so asto give a firm bond between the substrate and the film. When usingadhesives which are solid at room temperature, the procedure is similar.If liquid adhesives are employed, the procedure is generally that theliquid adhesive is applied to the substrate and the coated plastic filmis laminated onto the heated substrate that has been coated with theadhesive.

The invention is illustrated in more detail in the working examplesbelow. All percentages and parts are to be understood as being by weightunless expressly stated otherwise.

EXAMPLE 1

A white pigmented thermoplastic polyurethane film 60 μm thick(Elastollan® EL 1184A from Elastogran GmbH) is fixed on a metal sheetand coated with a customary commercial white pigmented nonaqueous topcoat (dry film thickness: 20 μm). The base coat is baked at 130° C. for30 minutes. A transparent polyester film (Melinex®, ICI), which has beenprovided with a 20-μm thick adhesion promoter layer comprising apolyester based on 1,4-butanediol and terephthalic/isophthalic acid(1:1) is pressed onto the coated side of the film coated in this way, ata temperature of 150° C. and a pressure of 25 bar. The resultinglaminate is detached from the metal base and laminated at a temperatureof 220° C. and a pressure of 50 bar onto a bodywork panel (Bonder 2660OC).

EXAMPLE 2

The adhesion promoter layer of a white pigmented, thermoplasticpolyurethane film 60 μm thick (Elastollant® EL 1184A from ElastogranGmbH) which has been provided with a 20-μm thick adhesion promoter layercomprising a polyester based on 1,4-butanediol andterephthalic/isophthalic acid (1:1) is covered with a release paper. Theside of the film which has not been covered is then coated with acustomary commercial white pigmented nonaqueous paint (dry filmthickness: 20 μm). The base coat is baked at 130° C. for 30 minutes. Atransparent polyester film (Melinex®, ICI) which has been provided witha 20-μm thick adhesion promoter layer comprising a polyester based on1,4-butanediol and terephthalic/isophthalic acid (1:1) is pressed ontothe coated side of the film coated in this way, at a temperature of 150°C. and a pressure of 25 bar. After removing the release paper, theresulting laminate is laminated at a temperature of 220° C. and apressure of 50 bar onto a bodywork panel (bonder 2660 OC).

Testing the Coated Substrates

The coated substrates produced in accordance with Examples 1 and 2showed excellent resistance values both in the VDA [German Automakers'Association] stone chip test (2×500 g at 2 bar) and in the Mercedes Benzball shot test (VDA: rating 1; ball shot test: degree of rusting=0,degree of flaking: ≦2 mm²). To test the corrosion resistance, the coatedsubstrates were scribed with a slit about 10 cm long extending down tothe metal panel, and were subjected to a salt spray test in accordancewith DIN 50 021. After 6 weeks no scribe creep was evident.

What is claimed is:
 1. A film coated with two or more coats, comprisingAa coated plastic film consisting of a plastic base film having a surfaceand a thickness of from 10 to 500 μm and a filler composition coated onthe surface of the plastic base film, B at least one pigmented paintcoat coated on the coated plastic film, and C a transparent plastic filmcoated on the pigmented paint coat.
 2. The film of claim 1, wherein aplastic film which can be peeled off is applied over an uncoated side ofthe base film.
 3. The film of claim 1, wherein the transparent plasticfilm is resistant to UV light.
 4. The film of claim 1, wherein anadhesion promoter layer is arranged between the transparent plastic filmand the paint coat.
 5. The film of claim 1, wherein the plastic basefilm is a thermoplastic polyolefin film or a thermoplastic polyurethanefilm.
 6. The multicoated film of claim 1, wherein the plastic film basecomprises a polymer selected from the group consisting of polyurethane,polyolefin, polyamide, polyester, polyacrylate, polycarbonate, and amixture thereof.
 7. A process for producing moldings coated with thefilm claim 1, comprisingA coating a plastic film having a thickness of10 to 500 μm and a surface with a filler coat composition, B overcoatingthe surface of the filler coat with at least one pigmented paint coat, Ccoating the pigmented paint coat with a transparent plastic film, Dcuring the applied paint coats to provide a coated film, E laminatingthe coated film thus prepared onto a substrate, and F producing moldingsfrom the substrate coated in this way.
 8. The process of claim 7 whereinthe substrate is a metal sheet.
 9. The multicoated film of claim 1 whichhas sufficient flexibility to be rolled up.
 10. The multicoated film ofclaim 9 having a T-bend value of ≦3.0.
 11. A process for preparing afilm coated with two or more coats, comprisingA coating a surface of aplastic base film having a thickness of from 10 to 500 μm, with a fillercoat composition, B overcoating the surface of the filler coat, with atleast one pigmented paint coat, C coating the pigmented paint coat witha transparent plastic film, and D curing the applied paint coats. 12.The process claim 11, wherein the filler coat is cured before beingovercoated with at least one pigmented paint coat.
 13. The process ofclaim 11, wherein a plastic film which can be peeled off is appliedafter step C.
 14. The process claim 11, wherein the plastic film of stepA comprises a film selected from the group consisting of thermoplasticpolyolefin film, thermoplastic polyurethane film and mixtures thereof.15. A process for producing moldings coated with the film of claim 1,comprising providing a substrate,A coating the substrate with a plasticfilm having a thickness of 10-500 μm and a surface, B coating thesurface of the plastic film with a filler coat composition, Covercoating the surface of the filler coat with at least one pigmentedpaint coat, D coating the pigmented paint coat with a transparentplastic film, E curing the applied paint coats, and F producing moldingsfrom the substrate coated in this way.
 16. A process for producingmoldings coated with the film of claim 1, which comprisesA laminating aplastic film having a thickness of from 10 to 500 μm onto a substrate, Bproducing moldings from the substrate coated in this way, C coating thesurface of the plastic film with a filler coat composition, Dovercoating the surface of the filler coat with at least one pigmentedpaint coat, E coating the pigmented paint coat with a transparentplastic film, and F curing the applied paint coats.
 17. The process ofclaim 16 wherein the substrate is a metal sheet.
 18. The process ofclaim 15 wherein the substrate is a metal sheet.